Thor's Banishment

After the battle against the Frost Giants, destroying the fragile truce between them and the Asgardians, Odin punished Thor by stripping him of his godly powers. Odin exiled Thor to Earth as a mortal, accompanied by his hammer Mjølnir, now protected by an enchantment spoken by Odin so that only a worthy person can wield its power. Both were transported to Puente Antiguo, New Mexico.[1]

When Thor discovered Mjølnir's nearby location, he attempted to retrieve it from the facility that S.H.I.E.L.D. quickly constructed around the hammer, but he found himself unable to lift it, and was captured. With the help of Erik Selvig, he was freed and resigned himself to his exile on Earth.

Later, Loki, invisible to mortals, came to the facility where he attempted to lift the hammer, but he could not. When he seized the throne of Asgard, he sent the Destroyer to Earth to kill Sif, the Warriors Three, and Thor. The Destroyer attacked and defeated the Asgardian warriors, prompting Thor to sacrifice himself instead. Struck by the Destroyer and near death, Thor's sacrifice proved him worthy to wield Mjølnir. The hammer returned to him, restoring his powers and enabling him to defeat the giant automaton.

Thor returned to Asgard where he stopped Loki's plan to destroy Jotunheim. To do that, he had to destroy the Bifrost Bridge with Mjølnir.[1]

Some time later, when Loki reappeared on Earth, Thor came to capture him. Loki was captured by Iron Man and Captain America, but they were not willing to hand him over to Thor. Thor fought against them, but even Mjølnir was powerless against Captain America's Shield.

While in battle against the Hulk, Thor used Mjølnir to knock the Green Goliath off his feet. When Thor threw Mjølnir, the Hulk tried to catch it only to be dragged straight down to the ground with him. Even with all his strength, the Hulk was unable to lift Mjølnir, giving Thor an upper hand in the fight.

After joining forces with the Avengers, Thor used Mjølnir to great effect against the Chitauri Army. It was however unable to disarm the Tesseract. On the battlefield, Thor used Mjølnir to throw lightning at the Chitauri portal, bringing down a Leviathan and to simply kill potentially hundreds of Chitauri.[5]

Return of the Dark Elves

Thor also used Mjølnir against the Marauders during the Marauders' War, notably destroying a Kronan with one hit, as well as the Dark Elves when they invaded Asgard. Mjølnir was also used to throw lightning at Malekith, burning the right side of his face.

When dealing with the Aether, Mjølnir's lightning managed to shatter it into shards, only for it to reform later. Mjølnir was also no match against the Kursed Algrim who simply deflected it when Thor summoned it to strike him. Mjølnir, however worked greatly against Malekith on Earth, with Thor being able to deflect many of his Aether powers. The constant shifting of the fighting between worlds caused Thor and the hammer to become separated, but at the battle's apex, as Malekith unleashed the Aether to complete his plan, Thor was able to summon Mjølnir back to his hand and use it to bury the last of Erik Selvig's gravitational devices into Malekith's chest, allowing Jane Foster to transport the Dark Elf warlord to his death on Svartalfheim.

Thinking he was talking to his father (though it was Loki in disguise), Thor offered Mjølnir back to "Odin" who refused it.[6]

Following the battle, the Avengers organized a party at the Avengers Tower to celebrate the recovery of Loki's Scepter and the defeat of Wolfgang von Strucker. A game to see if anyone could lift Mjølnir was played. Only Captain America managed to move the hammer slightly, much to Thor's discomfort.

Running at superspeed, Quicksilver saw Mjølnir fly past him as Thor threw it during the Battle at the Salvage Yard. Planning to use it against the Avengers, Quicksilver grabbed the flying hammer; it dragged him across the facility until he released it. Captain America was able to use that opportunity to knock out the dazed and confused opponent.

Acting on a vision he had received, Thor used Mjølnir to recharge the Cradle containing Ultron's incomplete biological body, resulting in the birth of the Vision. A few moments later, as the Avengers were debating whether they could trust him, the Vision easily lifted Mjølnir and casually handed it to Thor. Since the hammer had judged him worthy, Thor accepted the android as an ally and, later, advised he be allowed to continue to be entrusted with the Mind Stone.

Mjølnir was once again used in conjunction with Captain America's Shield to create a combination attack that destroyed many Ultron Sentries as the Battle of Sokovia waged. Captain America would throw his shield and allow Thor to hit it with Mjølnir, causing the shield to fly faster as a projectile weapon.

Vision's ability to use the hammer was utilized during the Ultron Offensive, who of course was not expecting anyone besides Thor to use it. Vision commented that Mjølnir was "terribly well-balanced", which Thor said was necessary so that its wielder did not lose momentum on forward swings.[7]

Capabilities

"Forged in the heart of a dying star, its power has no equal, as a weapon to destroy or as a tool to build. It is a fitting companion for a king."

Thor has been entrusted with the mighty hammer Mjølnir, that was forged in the heart of a dying star. Thor's mystical hammer Mjølnir, which resembles a mallet rather than a war hammer, has a number of elemental powers. It has been stated by Odin himself that Mjølnir's power has no equal. Made of Uru, Mjølnir itself is extremely durable, like the Earth metal vibranium, and combined with the various enchantments placed upon it by Odin, it is, for all intents and purposes, indestructible. It has deflected three blasts from the Destroyer (which were able to disintegrate anything that they hit) and return a blast back to the Destroyer. Thor often uses the hammer as a blunt melee weapon, with almost nothing being capable of withstanding a hammer strike or throw (with the exception of Captain America's Shield). Thor used Mjølnir for a variety of short- and long-range attacks, either by direct hits or by throwing it. It returned to Thor whenever he threw it or summoned it, regardless of the impending obstacles and distance; even traveling through realms. Whenever dropped by Thor, it assumed a fixed position from which no one could move it except for a "worthy" individual. Those worthy of wielding Mjølnir will find swinging the hammer nearly effortless, as Vision states it is "terribly well-balanced". Thor also used it for directing his summoned elements, such as lightning, wind, rain, and snow. A few examples of the abilities Thor has shown with Mjølnir are:

Weather Element Control: Wielding Mjølnir grants Thor the ability to control the base elements of a storm. It can control the elements and can create giant, raging, electrical storms complete with thunder, lightning, hurricane-force winds, tornadoes, tidal waves, earthquakes, and torrential rains on a moment's notice, with lightning being most commonly used. He summoned a Class-5 Tornado to battle the Destroyer, a great lightning bolt powerful enough to destroy a large piece of landscape in Jotunheim, a lightning bolt to knock down Loki on the Bifrost bridge, and control the elements. One notable use of lightning was during Thor's fight with Iron Man, where he struck Iron Man with a bolt of lighting, which was supposed to knock Iron Man over. However, to the surprise of both parties, this attack only knocked Iron Man back slightly, while simultaneously charging the armor's power reserve to 475%. He was able to shoot a massive lightning bolt at the portal of the Chitauri to prevent any more reinforcements, destroying many Chitauri soldiers and a Leviathan at one go. The Norse myths and legends regarded him as a Thunder God because of the hammer's influence over the weather.

Lightning Manipulation: Mjölnir is able to generate and manipulate lightning, which Thor uses as a weapon. Its lightning can manifest as powerful blasts strong enough to destroy a large piece of landscape in Jotunheim. It can be harnessed to enhance physical strikes with the hammer, enough to cause electrical shockwaves that can decimate and level the surface it hits. Thor has used lightning to knock down Loki on the Bifrost bridge, shoot Iron Man that boosted his armor's power reserve to +400% and took down a Chitauri with a single thunderbolt. Thor also shot a massive lightning bolt at the portal of the Chitauri to prevent anymore re-enforcements.

Physical Empowerment: Though Thor's Asgardian physiology far exceeds the abilities of a normal athletic human, when he was stripped of his power and found unworthy of Mjølnir, his godlike abilities diminished so much that he was able to be tasered into unconsciousness. It was only when he was found worthy of wielding Mjølnir did Thor recover his godlike physiology and therefore can go toe to toe with potent beings like the Destroyer. Thus the hammer enhances a person's physiology to that of Thor, the god of lightning.

"But if you put the hammer in an elevator...""...the elevator will still go up.""And an elevator is not worthy."

Worthiness Enchantment: After Thor disobeyed Odin and nearly caused a war between Asgard and Jotunheim, Odin banished Thor to Earth, without his powers, and placed an enchantment on the hammer Mjølnir. "Whosoever holds this hammer, if he be worthy, shall possess the power of Thor." This enchantment surrounding Mjølnir prevents it from being wielded by anyone save those who have been found worthy enough to wield. When Thor sacrificed himself to protect Earth from the Destroyer, he proved himself worthy to wield Mjølnir once again and gained full use of his powers. Thor and Odin were, for some time, the only individuals capable of lifting it, although Steve Rogers apparently showed the potential to be worthy as he moved the hammer slightly, most likely due to his innocence during his childhood and always being someone who protects for the good of everyone. Vision, however, ultimately proved to be able to lift and use the hammer with as much ease as Thor, but none of the citizens of Puente Antiguo could lift it, nor could Loki. Not even the Hulk's incredible strength could lift Mjølnir.

Clothing Generation: By summoning lightning from the sky into Mjølnir, whatever Thor is wearing would be instantly transformed into his battle armor. In one instance, the lighting blasted onto him restored his powers and completely healed him from fatal injuries inflicted by the Destroyer.

Weapon Summoning: Mjølnir obeys Thor's summons as though it were alive. Mjølnir went to Thor when it was in a crater from miles away, reaching him in seconds. Mjølnir will return to Thor whenever he throws it at an opponent. While battling the Hulk in a hanger of the Helicarrier, Thor summoned Mjølnir from another room and it came crashing through the Helicarrier to get to him. After Mjølnir is hurled, Thor can also change the hammer's direction inflight easily.

Flight: Thor is capable of hurling Mjølnir with great force and, by holding onto the leather thong or strap, is capable of flying through the air at tremendous speeds. How fast is not specified, but he was able to remain aloft in the middle of a Class-5 tornado, and traverse the distance from his father's chambers to Heimdall's Observatory and back again in seconds. He used Mjølnir to fly into combat against Iron Man in the woods, to fly to the top of a skyscraper and on top of a Chitauri warship. However, due to Mjølnir's ability to stay airborne only when moving continuously, Thor is unable to stay stationary airborne.

Weight Manipulation: Mjølnir's enchantment allows its worthy wielders to swing it nearly effortlessly yet in reality it is as heavy as a mountain to an average person. Its ability to manipulate its weight allows Mjølnir to fly at high speeds without slowing down when hurled as well as have it hit with a massive concussive force equal to at least that of a grenade. In Jotunheim, he bashes the Frost Giants around him with his war hammer, then throws Mjølnir, making it hit multiple Frost Giants in its path in moments. Quicksilver and Hulk were pinned down by Mjølnir's awesome weight. Mjølnir's momentum can also be manipulated. If held by someone worthy, its momentum will be that of a simple hammer. If caught and held by someone unworthy in mid-air after being thrown by someone worthy, its momentum will be that of a heavily-weighted object with its velocity unchanged.

Energy Projection: With Mjølnir, Odin channeled and projected a powerful blast of energy, using it to take away all of Thor's superhuman powers and destroying what was left of Thor's armor after stripping much of it off him and throwing him into the Bifrost to Earth.

Trivia

In the comics, the hammer's name translates as "The Crusher" or "The Grinder". However, in Norse mythology, its name translates as "That which smashes".

Odin mentions that the hammer can also be used as a tool to build, yet no such use of Mjølnir has been seen yet in the MCU. This is presumably only symbolic, as a hammer can be a tool as well as a weapon.

The MCU pronunciation for Mjølnir is ME-ol-near.

Darcy Lewis has always mispronounced the hammer's name as "Mew-mew" or "Myeu-muh".